Control system for exhaust gas recirculation system

ABSTRACT

A system and method for controlling an exhaust gas recirculation system ( 10 ) on an electronically controlled, turbocharger ( 18 ) equipped internal combustion engine ( 12 ) having two or more actuating devices ( 84,86 ). In the disclosed embodiments, the actuating devices ( 84,86 ) may include an exhaust gas recirculation valve ( 40 ), a turbocharger back pressure valve ( 44 ), the vane actuators ( 46 ) in a variable geometry turbocharger ( 48 ), or an air intake throttle valve.

This is a continuation-in-part of application Ser. No. 08/888,167, filedJul. 3, 1997 and issued Jun. 30, 1998, U.S. application Ser. No.5,771,867.

TECHNICAL FIELD

The present invention relates to emission control system for an internalcombustion engine, and more particularly, to exhaust gas recirculation(EGR) control system and apparatus for internal combustion engines whichwill operate to minimize NOx and other emissions while minimizingparticulate matter emissions from internal combustion engines.

The present invention generally relates to a system and technique forcontrolling a pair of actuators in an EGR system of an internalcombustion engine and, more particularly, is concerned with an enginecontrol strategy for improving responsiveness and the operatingcharacteristics of the actuators.

BACKGROUND ART

Exhaust gas recirculation is a technique commonly used for controllingthe generation of undesirable pollutant gases and particulate matter inthe operation of internal combustion engines. This technique has provenparticularly useful in internal combustion engines used in motorvehicles such as passenger cars, light duty trucks, and other on-roadmotor equipment. The exhaust gas recirculation technique primarilyinvolves the recirculation of exhaust gas by-products into the intakeair supply of the internal combustion engine. The exhaust gasreintroduced to the intake manifold and subsequently the enginecylinders reduces the concentration of oxygen therein, which in turnlowers the maximum combustion temperature within the cylinder,decreasing the formation of nitrous oxide. Furthermore, the exhaustgases typically contain a portion of unburned hydrocarbon which isburned on its reintroduction into the engine cylinders, which furtherreduces the emission of exhaust gas by-products which would be emittedas undesirable pollutants from the internal combustion engine.

However, it is necessary to carefully control the proportion ofrecirculated exhaust gas to intake air. For example, while a greaterproportion of exhaust gas may be recirculated at low load levels, it isnecessary to ensure that the proportion of recirculated exhaust gas doesnot become excessive, causing the engine to stop due to a lack ofsufficient oxygen to mix with the fuel so as to permit combustion. Onthe other hand, if the proportion of exhaust gas recirculated at fullengine load is excessive, the power output of the internal combustionengine is reduced, and the engine will typically emit undesirablequantities of smoke and particulate matter due to unsatisfactorycombustion in the engine cylinders. Therefore, it is clear that theexhaust gas recirculation process is desirably tightly controlled.

Another technique useful in the control and reduction of undesirableemissions from internal combustion engines is the use ofpressure-charged intake air. This permits the use of relatively smallercubic displacement and lighter weight internal combustion engines inmobile equipment, reducing in turn the specific fuel consumption of thevehicle and overall mass of the vehicle necessary to perform a givenfunction. In addition to the benefits of reduced size and mass, thetypical pressure-charging device may be controlled to provide improvedemissions characteristics. Pressure-charging machines suitable for suchapplications include the exhaust gas driven turbocharger which iscomprised typically of an exhaust gas driven turbine linked to acompressor disposed in the intake air stream to provide compression ofthe intake air. One way of controlling a turbocharger is to provide agate which controls exhaust gas flow and gates exhaust gas to bypass theexhaust gas turbine and control the charging rate of the turbocharger sothat the maximum pressure limits of the associated internal combustionengine are not exceeded. Another means of controlling a turbocharger isto provide a variable geometry turbocharger which allows for variationof the turbocharger vane position in response to engine speed or engineload or both. Change in vane position affects the manifold pressureswithin the engine air system which in turn affects the recirculationrate of exhaust gases from the exhaust manifold to the intake manifold.

Current EGR systems are generally used when an exhaust manifold pressureis greater than the pressure in the inlet manifold. In a pressurecharged engine, including turbocharged and supercharged engines asexamples, the pressure in the inlet manifold typically increases as theengine load increases. As the pressure in the exhaust manifoldapproaches the pressure in the inlet manifold, the exhaust gasrecirculation flow in a fixed diameter orifice or duct between the inletmanifold and the exhaust manifold decreases. Higher engine speeds andengine loads also generally result in an increase in NOx emissions.Conventional EGR systems provide little, if any, exhaust gasrecirculation during times when the engine is producing the most NOx,because the low pressure differential between the exhaust manifold andthe inlet manifold prevents sufficient exhaust gas from entering theinlet manifold. Thus, EGR flow rate and turbocharger boost pressurerepresent engine operating parameters that are indirectly linked, yetoften independently controlled. The present invention is aimed atovercoming the aforementioned problems.

DISCLOSURE OF THE INVENTION

The present invention is a system and method for controlling an exhaustgas recirculation (EGR) system in an internal combustion engine havingtwo or more actuating devices on a pressure-charged internal combustionengine. In the various disclosed and/or contemplated embodiments, theactuating devices may include an air intake throttle valve, an exhaustgas recirculation (EGR) valve, an EGR bypass valve, a turbocharger backpressure valve, and/or the adjustable turbine blades in a variablegeometry turbocharger.

In one aspect, the present invention may be characterized as a controlsystem for an engine exhaust gas recirculation system having two or moreactuating devices. The disclosed control system includes a pair ofactuators and a controller adapted for receiving two or more engineoperating parameter inputs and providing two or more actuator controloutput signals. In a disclosed embodiment, the first actuator is coupledto the controller and is adapted for receiving, as an input, a firstactuator control output signal from the controller which is based, inpart, on the engine operating parameter inputs. The first actuator isfurther connected to a first actuating device, such as an exhaust gasrecirculation system and is adapted for controlling the first actuatingdevice in response to the first actuator control output signal. Thedisclosed embodiment also includes a second actuator coupled to thecontroller and having an input for receiving a second actuator controlsignal from the controller. As with the first actuator, the secondactuator is further connected to a second actuating device of theexhaust gas recirculation system and is adapted for controlling thesecond actuating device in response to the second actuator controloutput signal. The second actuator control output signal is generated bythe controller based on a variance signal or similar such feedback fromthe first actuator together with the engine operating parameter inputs.Using the feedback, the first and second actuators are operativelycoupled. In other words, the second actuator is responsive when thefirst actuator command signal exceeds prescribed actuator limits to thefirst actuator. However, when the first actuator is commanded oroperating within the prescribed actuator limits, the variance orfeedback signal is zero and the second actuator operates more or lessindependently of the first actuator.

The present invention may also be characterized as a method ofcontrolling an exhaust gas recirculation system having two or morecooperatively controlled actuating devices. The disclosed methodinvolves the steps of: (1) receiving two or more engine operatingparameter inputs; (2) producing an actuator command signal in responseto the engine operating parameter inputs; (3) producing an actuatorcontrol output signal based on the actuator command signal andprescribed actuator limits which are based, in part on the engineoperating parameter inputs; and (4) controlling the first actuator inresponse to the actuator control output signal. The disclosed methodfurther includes the steps of: (5) producing an actuator variance signalthrough the comparison of the actuator control output signal and theactuator command signal; (6) producing a second actuator control outputsignal based on the variance signal and the engine operating parameterinputs wherein the second actuator is controlled in response to thesecond actuator control output signal. Using the presently disclosedmethod, the first and second actuators are cooperatively controlled inthat the second actuator is actively controlled when the first actuatorcommand signal exceeds the prescribed actuator limits thereby producinga variance signal. When the first actuator is operating within theprescribed limits, the variance signal is zero (i.e. control outputsignal is equal to command signal) and the second actuator operatesindependently of the first actuator.

These and other aspects, features and advantages of the invention willbecome apparent to those skilled in the art upon a reading of thefollowing detailed description when taken in conjunction with thedrawings illustrating various embodiments of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 discloses schematically an exhaust gas recirculation systemaccording to the present invention as employed in a representativeinternal combustion engine having a turbocharger as the air intakepressurizing device wherein the system cooperatively controls an exhaustgas recirculation (EGR) valve in conjunction with the turbocharger backpressure valve.

FIG. 2 discloses yet another embodiment of an exhaust gas recirculationsystem employed in a representative internal combustion engine having aturbocharger as the air intake pressurizing device and wherein thesystem cooperatively controls an exhaust gas recirculation (EGR) valvein conjunction with the actuator of a variable geometry turbocharger.

FIG. 3 is a general block diagram of the exhaust gas recirculationcontrol system in accordance with the principles of the presentinvention.

DESCRIPTION OF THE PREFERRED EMBODIMENT

The following description is of the best mode presently contemplated forcarrying out the invention. This description is not to be taken in alimiting sense, but is made merely for the purpose of describing thegeneral principals of the invention. The scope and breadth of theinvention should be determined with reference to the claims.

Turning now to the drawings and particularly to FIG. 1 there is shown aschematic representation of an exhaust gas recirculation (EGR) system 10for a turbocharged compression ignition engine 12 (i.e. diesel engine).As seen therein, the turbocharged compression ignition engine 12includes an intake manifold 14, exhaust manifold 16, a turbocharger 18,and an air-to-air aftercooler 20. The turbocharger 18 having an exhaustgas driven turbine 22 coupled to an intake air compressor 24. Theturbocharger 18 also includes an exhaust gas inlet 26 and an exhaust gasoutlet 28 both in fluid communication with the exhaust gas driventurbine 22. The turbocharger 18 further includes a fresh intake airconduit 30 and a compressed air exit conduit 32 both of which are influid communication with the air compressor 24.

In the preferred embodiment, the EGR system 10 includes an EGR conduit34 and an optional EGR cooler. As seen in FIG. 1, the EGR conduit 34 isdisposed in fluid communication with the exhaust manifold or a selectnumber of combustion chambers and is adapted for diverting a flow ofexhaust gas from the exhaust manifold to a position downstream of theturbocharger 18 and air-to-air aftercooler 20 and proximate the intakemanifold 14. The diverted flow of exhaust gas from the exhaust manifoldvia the EGR conduit 34 is controlled using one or more EGR valves 40operatively associated with an engine controller 80 or similar suchengine control module.

The engine controller 80, as is known to those skilled in the art, willtypically contain various means for controlling the operation of theengine in response to sensed measurements of various operatingparameters of the engine as provided to the controller 80 by varioussensors disposed on and in conjunction with the engine. As it relates tothe present EGR system, the controller 80 is provided with a means forsensing the operating speed and load of the engine by way of meansgenerally known to those skilled in the art. The engine controller 80 isalso adapted for controlling the fuel injector (not shown), to controlthe quantity, timing, and duration of fuel injected into the combustionchamber of the engine. The engine controller 80 is often adapted forcontrolling the air intake valves (not shown) and exhaust valves (notshown) associated with each of the engine cylinders.

In addition to controlling the air and fuel systems of the engine, theengine controller 80 is a processor based device or means for providingcontrol of an exhaust gas recirculation (EGR) system of the engine,providing independent and simultaneous control of the EGR valve 40 andthe turbocharger back pressure valve 44. In a preferred mode ofoperation, the controller 80 actuates the EGR valve 40 to a prescribedposition prior to actuating the back pressure valve 44 therebyoptimizing the recirculation of exhaust gas to the combustion chamber atprescribed engine speeds and loads. As the load demand on the engineincreases, the controller 80 continuously actuates the EGR valve 40 andthe turbocharger back pressure valve 44 to cause a continuous transitionof control from the EGR valve 40 or first actuating device to theturbocharger back pressure valve 44 or second actuating device. Thiscooperative control of both the EGR valve 40 and the turbocharger backpressure valve 44 permits the controller 80 to function as a closed loopcontroller on these elements, for permitting precise and responsivecontrol of the exhaust gas recirculation rate through the exhaust gasrecirculation conduit 34 in most operating modes of the engine.

The embodiments of FIG. 2 is very similar from a structural andoperation standpoint, to the embodiment of FIG. 1. The notabledifferences include the turbocharger and the controlled actuatingdevices. The principle of operation or cooperation between two actuatingdevices of the EGR system, however, are quite similar for bothembodiments. For example, in the embodiment illustrated in FIG. 2, theintake air pressurizing device is preferably a variable geometry exhaustgas driven turbocharger 48 and the first actuating device is the exhaustgas recirculation (EGR) valve 40 operatively associated with an EGRconduit 34. The embodiment of FIG. 2 however, contemplates using thevariable geometry turbocharger vane actuators 46 as the second actuatingdevice.

The basic control of a variable geometry turbocharger is realized byactuating or adjusting the position of the vanes of the turbine. In thismanner, as the engine goes through a change in load the vanes on theturbocharger close or open to some prescribed position or limits inaccordance with various engine operating maps or look up tables foundwithin the engine controller 80. Closing the vanes cause theturbocharger to spin faster for a given air flow and thereby increasesthe intake manifold pressure. Increasing the intake manifold pressure inturn affects the EGR flow rate. Conversely, opening the turbochargervanes operates to slow the spin of the turbocharger and decrease theintake manifold pressure which likewise affects the EGR flow rate. It isimportant to note that changing the EGR flow rate in turn affects theexhaust gas flow to the turbocharger so that it becomes that much moreimportant to precisely and cooperatively control exhaust gas flowthrough the turbocharger as well as EGR flow to the intake manifold.

Referring now to FIG. 3, there is shown a functional block diagram ofthe preferred or contemplated control system, generally designated bythe numeral 81. As illustrated, the EGR control system 81 is operativelycoupled to a pair of actuators 84, 86 for controlling the operationselected mechanisms such as air or exhaust flow valves associated withthe engine. In the illustrated embodiment, the actuators 84, 86 areoperatively coupled to an EGR valve 40 and a second actuating devicesuch as a turbocharger back pressure valve or a vane actuator of avariable geometry turbocharger. The disclosed EGR control system 81 alsoincorporates a feedback loop wherein one of the actuator control signaloutputs is used as an input to the control of the other actuator. TheEGR control system 81 also utilizes one or more measured engineoperating parameters as input signals. In the present embodiment, theEGR control system 81 utilizes measured parameters such as the enginespeed and engine load. Similar such engine operating parameters such asengine operating temperatures, coolant temperatures, air mass flow, fuelmass, air intake temperatures, throttle position, and the like, can alsobe used.

In the illustrated embodiment, the EGR control system 81 operates bydetermining a EGR valve target position 87 based on selected engineoperating parameters such as the measured engine speed 88 and thedesired fuel mass 90 which generally corresponds to engine load. The EGRvalve target position 87 is then converted to an EGR actuator voltagesignal 92. Concurrently, the intake manifold conditions and air massflow conditions are ascertained 94 from appropriate engine operatingsensors 82. The measured engine speed 88 and the fuel mass 90 parametersare used as inputs together with the engine intake manifold conditionsand air mass flow conditions to yield an intake variance signal 100.

The intake variance signal 100 together with the EGR actuator voltagesignal 92 are forwarded to the EGR controller 102 for determining thecommanded EGR actuator signal 104. The commanded EGR actuator signal 104is forwarded to an EGR limiter 106 which adjusts, if necessary, thecommanded EGR actuator signal 104 to fall within prescribed limits 107.The prescribed limits 107 are preferably determined using various engineoperating parameters such as the aforementioned engine speed 88 andengine load 90 parameters. The adjusted or corrected EGR actuator signal108 is then forwarded to the EGR actuator 84 thereby commanding the EGRvalve 40 to the appropriate position.

A feedback signal 110, representing the corrected EGR actuator signal,is then compared to the commanded EGR actuator signal 104 to yield anEGR actuator variance signal 112. Any variance between the corrected EGRactuator signal 108 and the commanded EGR actuator signal 104 isembodied in the EGR actuator variance signal 112 which is used as aninput to the turbocharger valve controller 120. Concurrently, thecontrol system 81 is also determining a turbocharger valve targetposition 122 based on the selected engine operating parameters such asthe measured engine speed 88 and the desired fuel mass 90 or engineload. The turbocharger valve target position 122 is converted to aturbocharger actuator voltage signal 124 which, along with the EGRactuator variance signal 112, are input to the turbocharger valvecontroller 120 for purposes of determining the commanded turbochargeractuator signal 126. The commanded turbocharger actuator signal 126 isforwarded to a turbocharger limiter 128 which adjusts, as required, thecommanded turbocharger actuator signal 126 to within prescribed limits130. As with the EGR limiter, the prescribed limits 130 for theturbocharger actuator 86 are preferably determined using various engineoperating parameters such as the engine speed 88 and fuel mass 90parameters. The corrected turbocharger actuator signal 132 is forwardedto the turbocharger actuator 86 thereby commanding the turbocharger backpressure valve 44 or the variable geometry turbocharger vane to theappropriate position.

Having commanded the EGR actuator 84 and turbocharger actuator 86 to thedesired positions, within the engine, the air flow mass and other engineoperating parameters are measured to yield the new inputs for thecontrol system 81. In this manner, the EGR control system 81 operates ina continuous manner at most engine operating conditions.

It can be seen that the subject invention provides a number ofadvantages including a reduction of harmful or undesirable emissions,such as particulate matter and NOx from the engine for a given speed andload. These advantages are realized due to the fact that the EGR valveis employed as a primary actuator for exhaust gas flow within theengine, with the turbocharger flow control devices (i.e. either backpressure valve or VGT vanes) providing a secondary and complementarycontrol of the exhaust gas recirculation rate. This permits the exhaustgas recirculation rate to be controlled by the engine controller acrossmost of the operating range of the engine.

From the foregoing, it should be appreciated that the present inventionthus provides a control system and apparatus for exhaust gasrecirculation system in an internal combustion engine. While theinvention herein disclosed has been described by means of specificembodiments and processes associated therewith, numerous modificationsand variations can be made thereto by those skilled in the art withoutdeparting from the scope of the invention as set forth in the claims orsacrificing all its material advantages.

What is claimed is:
 1. A control system (81) for an exhaust gasrecirculation system (10) having two or more actuating devices, saidcontrol system (81) comprising: an engine controller (80) adapted forreceiving two or more engine operating parameter inputs (88,90) andproviding two or more actuator control output signals (108,132); a firstactuator (84) coupled to said engine controller (80) and having an inputfor receiving a first actuator control output signal (108) from saidengine controller (80), said first actuator (84) further connected to afirst actuating device of said exhaust gas recirculation system (10) andadapted for controlling said first actuating device in response to saidfirst actuator control output signal (108); a second actuator (86)coupled to said engine controller (80) and having an input for receivinga second actuator control output signal (132) from said enginecontroller (80), said second actuator (86) further connected to a secondactuating device of said exhaust gas recirculation system (10) andadapted for controlling said second actuating device in response to saidsecond actuator control output signal (132); and wherein said enginecontroller (80) is adapted to generate said second actuator controloutput signal (132) based on said engine operating parameter inputs(88,90) and said control signals associated with said first actuator(84).
 2. The control system (81) of claim 1 wherein said first actuatingdevice is an exhaust gas recirculation valve (40).
 3. The control system(81) of claim 2 wherein said second actuating device is operativelyassociated with a turbocharger (18).
 4. The control system (81) of claim2 wherein said second actuating device is a turbocharger back pressurevalve (44).
 5. The control system (81) of claim 2 wherein said secondactuating device is a vane actuator (46) for a variable geometryturbocharger (48).
 6. The control system (81) of claim 2 wherein saidsecond actuating device (86) is an air intake throttle valve.
 7. Thecontrol system (81) of claim 1 wherein said engine controller (80)includes a processor and wherein said processor is adapted forgenerating a target position (87) for said first actuator (84) based onsaid engine operating parameter inputs (88,90,98).
 8. The control system(81) of claim 7 wherein said processor is further adapted for generatinga first actuator command signal (104) based on said target position (87)and said engine operating parameter inputs (88,90,98).
 9. The controlsystem (81) of claim 8 wherein said processor is further adapted forgenerating prescribed actuator limits (107) based on said engineoperating parameter inputs (88,90,98), and wherein said prescribedactuator limits (107) are used to adjust said first actuator commandsignal (104) to yield said first actuator control output signal (108).10. The control system (81) of claim 1 wherein said processor is furtheradapted for generating a target position (122) for said second actuator(86) based on said engine operating parameter inputs(88,90).
 11. Thecontrol system (81) of claim 10 wherein said processor is furtheradapted for generating prescribed actuator limits (130) for said secondactuator (86) based on said engine operating parameter inputs (88,90),and wherein said prescribed actuator limits (130) for said secondactuator (86) are used to adjust said second actuator control outputsignal(132).
 12. A method of controlling an exhaust gas recirculationsystem (10) in a turbocharged engine (12) having two or morecooperatively controlled actuating devices, said method comprising thesteps of: receiving two or more engine operating parameter inputs(88,90) producing a first actuator command signal in response to saidengine operating parameter inputs; producing a first actuator controloutput signal in response to said first actuator command signal and oneor more first actuator signal limits wherein said first actuator signallimits are determined based on said engine operating parameter inputs;controlling a first actuator in response to said first actuator controloutput signal; producing a second actuator control output signal inresponse to said first actuator control signal and said engine operatingparameter inputs; and controlling a second actuator in response to saidsecond actuator control output signal.
 13. The method of controlling anexhaust gas recirculation system (10) as set forth in claim 12 whereinsaid first actuating device is an exhaust gas recirculation valve (40).14. The method of controlling an exhaust gas recirculation system (10)as set forth in claim 12 wherein said second actuating device isoperatively associated with a turbocharger (18).
 15. The method ofcontrolling an exhaust gas recirculation system (10) as set forth inclaim 12 wherein said second actuating device is a turbocharger backpressure valve (44).
 16. The method of controlling an exhaust gasrecirculation system (10) as set forth in claim 12 wherein said secondactuating device is a vane actuator (46) for a variable geometryturbocharger (48).
 17. The method of controlling an exhaust gasrecirculation system (10) as set forth in claim 12 wherein said secondactuating device is an intake air throttle valve.